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Circuit Description Cont’d
The combiner also provides isolated signals to the gain/phase detector, providing 50dB of isolation between the signals, so that they
can be accurately sampled at the input of the gain/phase comparator without affecting each other. The gain/phase comparator
produces a DC voltage which is proportional to the log of the magnitude difference between its inputs, and another which is proportional
to the phase difference between the inputs. (The sign of phase is not attainable using the present gain/phase detector, but is relatively
easy to determine in operation by QSYing up a little and noting the direction of phase movement. I have developed a circuit for sign
detection, bu
t it would require a rather substantial change to the PCB. I may change to it in the future, but it wouldn’t be for quite
awhile). The phase/gain detector voltages are sampled by the A/D converter and the result is sent to the PIC over a Serial Peripheral
Interface.
Remaining connections to the PIC include switch inputs for the three front panel switches, interfacing to the GVFD display processor
and an SWR alarm relay which is used to kill the PTT to your amplifier to protect both the antenna and amplifier. The SWR alarm also
lights a front panel LED, and optionally can be jumpered to sound a piezo transducer. The PIC uses all these signals to calculate all the
various displayed parameters.
Finally, the PIC provides a standard RS-232 serial interface for remote control and monitoring of the LP-100A. Functions of the LP-
100A
can be controlled from a Windows® “Virtual Control Panel” program, either locally or over a network connection, including the
internet. The PIC’s firmware can also be updated through downloadable hex files which can be “flashed” into the PIC’s memory. A
program entitled MicroCode Loader (MCLoader), from Mecanique®, is provided to do this.
A Windows® charting program is also provided to allow graphing of any of the LP-100A
’s parameters including Z, R, X, SWR and
phase angle vs. frequency. The Plot program also offers a Smith Chart display, and I plan to add a translation function to allow for
automatic transformation of coupler load Z to antenna feedpoint Z. The programs will provide for inputting feedline length and type for
popular types of feedline. More on this is Appendix A.
Summary of Contents for LP-100A
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